كتاب الدعوات
17
The Book of Du'a (Supplications)
Abu Hurairah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ), "The supplication of every one of you will be granted if he does not get impatient and say (for example): 'I supplicated my Rubb but my prayer has not been granted'."

[Al-Bukhari and Muslim].

The narration of Muslim is: "The supplication of a slave continues to be granted as long as he does not supplicate for a sinful thing or for something that would cut off the ties of kinship and he does not grow impatient." It was said: "O Messenger of Allah! What does growing impatient mean?" He (ﷺ) said, "It is one's saying: 'I supplicated again and again but I do not think that my prayer will be answered.' Then he becomes frustrated (in such circumstances) and gives up supplication altogether."

وعنه أن رسول الله صلى الله عليه وسلم قال‏:‏ ‏ "‏يستجاب لأحدكم ما لم يعجل‏:‏ يقول‏:‏ قد دعوت ربي، فلم يستجب لي‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏ وفي رواية لمسلم لا يزال يستجاب للعبد ما لم يدعُ بإثم أو قطيعة رحم ما لم يستعجل‏.‏ قيل يا رسول الله ما الاستعجال‏؟‏ قال يقول قد دعوت وقد دعوت فلم أرَ من يستجب لي فيستحسر عند ذلك ويدع الدعاء‏.‏
Sunnah.com reference : Book 17, Hadith 35
Arabic/English book reference : Book 17, Hadith 1499